1. Technical Field
A method of fabricating semiconductor devices, and more particularly, to an oxynitride film is disclosed.
2. Background of the Related Art
A silicon oxide film (hereinafter called xe2x80x98pure silicon oxide filmxe2x80x99) in which a silicon substrate is oxidized within the oxidization furnace using a mixed gas of an oxygen (O2) gas or H2O and O2 has been used as a tunnel oxide film of the flash memory device. As the effective thickness of the tunnel oxide film required along with micronization of the device is reduced, however, it becomes difficult to satisfy the characteristic of the film required in the device with only the characteristic of the pure silicon oxide film.
Meanwhile, if the pure silicon oxide film is replaced by the oxynitride film, it is possible to secure characteristics of the film that were not satisfied by the pure silicon oxide film (for example, stress induced leakage current, the electric charge necessary for breakdown, the life of the film, etc.). This oxynitride film may be fabricated by a method by which the pure silicon oxide film of a give thickness is grown and a nitrification process is then implemented using NH3, N2O, NO, or the like to form a thin nitrogen layer at the existing silicon (Si)-silicon oxide (SiO2) film interface or a nitrogen-rich oxide film. If the nitrogen layer is formed at the Sixe2x80x94SiO2 interface by this method, the intrinsic properties of the film itself are improved but the concentration of the trap charge is increased in proportion to the concentration of nitrogen. For this reason, the carrier mobility in the channel of the transistor formed underlying it is influenced to change the threshold voltage of the transistor.
In particular, in case of NMOS, if the oxynitride film is used as the tunnel oxide film, the threshold voltage is dropped over 100 mV compared with the pure silicon oxide film even where the concentration of nitrogen at the Sixe2x80x94SiO2 interface is about 1 atomic %. Thus, it is difficult to secure the desired transistor characteristic. FIG. 1 is a graph illustrating the difference in the threshold voltage at the transistor using the pure silicon oxide film and the oxynitride film as the dielectric film. In FIG. 1, xe2x80x98axe2x80x99 indicates a case where the pure silicon oxide film is used as the dielectric film, and xe2x80x98bxe2x80x99 and xe2x80x98cxe2x80x99 indicate cases where the oxynitride film is used as the dielectric film. From FIG. 1, it could be seen that if the oxynitride film is used as the tunnel oxide film, the threshold voltage is dropped about 110 mV compared with the pure silicon oxide film when the concentration of nitrogen at the Sixe2x80x94SiO2 interface is dropped about 1.437 atomic %.
A method of forming an oxynitride film is disclosed which is capable of securing the characteristics of a film that are significantly improved than the characteristics of a film obtained in a pure silicon oxide film and minimizing variation in the threshold voltage of a transistor by a trap charge.
A disclosed method of fabricating an oxynitride film comprises loading a silicon substrate into an oxidization furnace, injecting an oxygen based source gas into the oxidization furnace to grow a pure silicon oxide film on the silicon substrate, stopping the injection of the oxygen based source gas and injecting an inert gas to exhaust or purge the oxygen based source gas remaining within the oxidization furnace, raising the temperature within the oxidization furnace to a nitrification process temperature, stabilizing the temperature within the oxidization furnace, implementing a nitrification process for the pure silicon oxide film by injecting a nitrogen based source gas, and stopping the injection of the nitrogen based source gas and heating the oxidation furnace to a higher temperature before rapidly cooling the oxidization furnace while injecting the inert gas into the oxidization furnace.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the claims.